Dopaminergic pathways and dopaminergic receptors are involved in dyskinesias, schizophrenia, and in the regulation of prolactin secretion. To better understand the physiological and pharmacological effects of dopamine, its agonists and antagonists, cultured pituitary lactotrophs which are excellent model for studying the initial dopamine-receptor interaction at the cell membrane level, as well as the subsequent events taking place inside the cells. Rat anterior pituitaries will be enzymatically dispersed and the cells will be cultured under sterile conditions. After 96 hours of culture, dopaminergic receptor characteristics will be investigated using tritium-labeled ligands such as (3H)-spiroperidol, (3H)-haloperidol and (3H)-dopamine. Specific binding will be determined by the use of excess (plus)-butaclamol. Unbound ligands will be aspirated and the attached cells with the bound (3H)-ligand will be stripped from the plates by trypsinization and counted. The following objectives will be pursued: 1) characterization of the dopamine receptor in terms of binding affinities, receptor density, binding kinetics and stereospecificity; 2) correlation of dopamine receptor occupation with prolactin secretion; and 3) changes in receptor affinity and/or number during different physiological states. An understanding of receptor physiology may lead to the development of drugs capable of modifying dopamine receptor binding. Additionally, dopamine agonists and antagonists could be developed for therapeutics of dyskinesias, psychoses, or prolactin endocrinopathies without adverse effects on other dopaminergic systems.